1. Field of the Invention
The invention relates to a method of applying a visible mark on one side of a hot steel slab.
2. Description of the Prior Art
A conventional way to mark a hot steel article is by writing by hand on the surface with a chalk stylus or waxy crayon that melts at high temperatures and leaves a permanent mark. This marking of a hot article is unsatisfactory because of the proximity of the person making to the hot article and the attendant danger to health which can lead to fatigue, inattentiveness and wrong marking. Because the work is monotonous the risk of errors is increased. When markings are absent, an ingot, bloom or slab is not indentifiable and is therefor declassified which involves a significant economic loss. Also the labour costs are high with such a method.
With an integrated steelplant a visible product-identification for the material flow between the steelplants and the rolling mills prevents interchanges of subjects.
Canadian patent specification No. 1043954 a method of applying a marking composition to a surface of a hot iron or steel article which composition is a dry powder suitable for application to the hot metal surface in dry powder form and consists of three components, which are a pigment, aluminium and adhesion agent, the aluminium powder serving to reduce the primary rolling oxide of iron, on the hot metal surface, thereby preventing or minimizing subsequent flaking off of the mark with underlying rust. The adhesion agent being effective to cause adhesion at a temperature which is not lower than 200.degree. C. The marking material adheres reliably and sufficiently tenaciously to survive subsequent treatment. The marking material can be applied by means of simple equipment and in a manner which permits the operator to be in a sufficient distance from the article for safety. The powder used in this known method should be in dry state and also the compressed air for its carrier gas jet is preconditioned to render it dry, so that during the marking on the hot metal no steam will be formed.
British patent specification No. 1534652 describes a method and apparatus for marking a hot steel slab on a roller table wherein the slab is previously scanned for the presence of doublings or other defects in the head and/or the tail thereof. In that method the slab is brought to a standstill on the roller table and at a relevant place or places on information derived from the scanning is provided with a visible mark by pneumatically projecting heat resistant marking powder only one side of the slab.
British patent specification No. 1541732 describes a method of applying a water based paint marking to a hot metal surface which comprises locally cooling the surface and applying the point marking to the locally cooled area. When an attempt is made to apply water based paint to a metal surface the temperature of which exceeds 900.degree. C., the paint does not mark the surface. This is due to film boiling of the paint. When the metal surface temperature on which the paint is being applied is below about 800.degree. C. the boiling becomes nucleate and paint particles can penetrate to the surface of the metal. Local cooling is preferably effected by two jets of air through two spaced cooling nozzles and the paint is preferably applied by a paint nozzle spraying through a stencil.